runlevel — Print previous and current SysV runlevel
runlevel [options...] 
runlevel prints the previous and current SysV runlevel if they are known.
The two runlevel characters are separated by a single space character. If a runlevel cannot be determined, N is printed instead. If neither can be determined, the word "unknown" is printed.
Unless overridden in the environment, this will check the utmp database for recent runlevel changes.
If one or both runlevels could be determined, 0 is returned, a non-zero failure code otherwise.
$RUNLEVELIf
                                $RUNLEVEL is set,
                                runlevel will print
                                this value as current runlevel and
                                ignore utmp.
$PREVLEVELIf
                                $PREVLEVEL is set
                                runlevel will print
                                this value as previous runlevel and
                                ignore utmp.